Conventionally, in a heat exchanger of an air conditioner or the like, internally grooved heat transfer tubes are generally arranged at a regular interval and a refrigerant flows therein. A tube axial direction and groove extending direction on the tube inner face form a certain angle (7°-30°), multiple grooves are processed to form ridges, and it is arranged that a fluid flowing in the tube is subjected to a phase transition (condensation and evaporation). In such a phase transition, the performance of the heat transfer tube has been improved by increasing a surface area in the tube, a fluid agitating effect by internal grooves, a liquid membrane retention effect between grooves by a capillary effect of the grooves, and the like (see, for example, Patent Document 1).